This invention relates to a method of forming an interlayer film, particularly to a method suited for forming an interlayer insulating film in manufacturing semiconductor devices.
In manufacturing semiconductor devices, a method is often adopted in which fluid source materials are used to form interlayer insulating films so as to fill up troughs on a substrate surface formed by wiring patterns thereon to assure a high smoothness of the substrate surface. When using the fluid source material for forming the interlayer insulating film, the fluid film, while it is being deposited, flows into the troughs between patterns from the top surfaces of the wiring patterns, resulting in filling the troughs.
When forming such an interlayer insulating film, a single step film deposition process is carried out in the related method to obtain the desired film thickness (for example, see M. Matsuura and M. Hirayama, 1995 Dry Process Symposium,.pp. 261-268 (1995)).
Such a method of forming interlayer insulating films, however, causes an undesirable phenomenon that, when the troughs on the substrate surface are formed by a plurality of patterns of differing widths, the thickness of the film formed on each of those patterns varies with dependence on pattern widths (hereinafter, this phenomenon is referred to as poor global smoothness), resulting in differences in level. This is considered to be as follows. When the film is deposited, the fluid film swells on each pattern due to the surface tension. On a wide pattern, the film swells more despite the fluid film flowing into the trough between patterns from the edge of the pattern as the film becomes thicker, so that when the film deposition ends, the film is formed with a thickness as swelled and results in becoming thicker than on a narrower pattern.
If an interlayer insulating film has such poor global smoothness, there occurs problems such as the step coverage of the formed interlayer insulating film becoming poor and a wiring layer or the like becoming thin partially when formed on the interlayer insulating film.
In view of foregoing, it is an object of this invention to provide a method of forming an interlayer film, which can eliminate the above phenomenon that the film formed on each pattern becomes uneven in thickness due to differences in width of those patterns formed on the substrate.